Manganese steel



nite

Mahwah, N.J., New

This invention relates to manganese steel and in particular to a standard 13% manganese steel so alloyed as to be capable of efiective precipitation hardening resulting in yield strength values of better than 70,000 psi. and elongation of at least about This represents, in comparison to the standard heat treated alloy, a significant enhancement in yield strength achieved at a sacrifice in elongation which is not deemed detrimental for many uses.

Manganese steel. is well known for the ease with which it can be work hardened. Precipitation hardening is not commonly followed. The practice, where followed, has been to solution heat treat at about 2000 F. followed by a quench or rapid cool to hold a metastable-austenitic structure. This preliminary step is the standard heat treatment for manganese steels as the mode of achieving maximum toughness. After this, the casing is aged at a temperature substantially under 2000 F. to precipitate a hardening phase, but the associated. loss in toughness attendant to such precipitation hardening procedure is usually too great to warrant general adoption. While the role of vanadium has heretofore been recognized in precipitation hardening, We have now found that the above specified values of yield strength and elongation can be attained in a precipitation hardened manganese steel by combining vanadium with nickel, or nickel and molybde-i num, provided that the carbon content does not exceed about 0.7%; in fact, superior results are achieved by holding carbon within the narrow range of 0.40.5%; and furthermore, wehave found that vanadium is so potent in increasing yield strength at a sacrifice of lowered ductility in a standard 13% manganese steel that its content should be restricted to not more than about 0.9% in conjunction With the aforesaid carbon limitation; and so to do is the primary object of this invention. Another object of the present invention is to so restrict the hardening treatment as to assure the desired results.

Exceptional results are achieved by limiting carbon to 0.40.5% and vanadium to 0.7-0.9%. The significance of this lowered carbon content can be best appreciated by realizing that carbon is usually specified as about ten percent of the manganese level which would therefore be about 1.2-1.4% for a standard 13% manganese steel. This combination, together with about 2% each of nickel and molybdenum in a standard 13-14% manganese steel (standard 13%) produces, after precipitation hardening, a yield strength of 90100,000 p.s.i. and an elongation of 2030%. This in comparison to the standard toughened alloy represents a doubling of yield at a sacrifice at the outside of only about half the ductility, and the accomplishment of this is another object of the present invention.

atent Patented Jan. 29, 1963 This preferred alloy can vary as follows:

0, Mn, Si, Ni, M0, V, P, S, Per- Per- Per- Per- Per- Per- Per- Percent cent cent cent cent cent cent cent 0.5 14. 3 0.8 2. 3 2.1 0. 9 Max. Max.

- 99,300 and 21.5% elongation. Eight hours at 1200 F.

raised the yield, but elongation was unacceptable at 9.5%. Aging at 1300 F. and 1400 F. for 6 hours also lowered ductility too far. I

The following table sets forth data pertinent to three alloys that represent the outside limits of carbon (0.7%)

and vanadium (about 0.3%) under the present invention:

TABLE I 0, Mn, Si, Ni, Cr, Mo, v, A1,

Heat Per- Per, Per- Per- Per- Per- Per- Per- 1 cent cent cent cent cent cent cent cent AS CAST Heat Yield 1 Tensile 2 Elong 3 RA. BEN

HARDENED BY 1,200 F., 2 HI(I)\IUGI)KS, VV.Q. (AFTER TOUGHEN- HARDENED BY 1,250 F., 2 l-lilQqllgts, W.Q. (AFTER TOUGHEN- HARDENED BY 1,300 F., 2 HI%UGIS, W.Q. (AFTER TOUGHEN- HARDENED BY 1,300 E, 6 H3353, W.Q. (AFTER TOUGHEN- TS 75. 6 2.5 11.6 286 79. 4 86. 3. l2. 3 179 75. 2 126. 5 33. 0 30. 5 262 HARDENED BY 1,300 F., 12 HOURS, AIR COOL 1 P.s.i. based on 0.2% set. 2 P.s.i. 10 3 Percent in 2. Percent.

6 Requirements of yield and elongation met.

The valuesforyield, tensile, elongation and reduction in area in Tables II and III- which follow are on the samebases as noted above in thefootnotes ofTable'I.

In view of our observation that high carbon contents (above about 0.7%) have a drastic eifect in lowering ductility,. it was concluded that the best combination of enhanced yield and not seriously impaired elongation would be found at even lower carbon levels,v provided carbon was-not-so :low as torequire having resort to sources of expensive manganese,- as distinguished from; ferromanganes'e, and more expensive alloying in general. Nickel; for instance is expensive and desirably is held to arninimum for reason. The iollowing heats,-therefore, represent'the preferred and least expensive form' of alloy practices underthe present invention,; and it shouldbe mentioned thatit wa's these heats 465 1555151115 above set forthrange for the preferred-alloy:

TABLE-1r Prc"cipz'tatz'on Hardenable Manganese- Chemical composition Heat No. 1

0, Mn, Si, Or. Ni, 'perperperperpercent cont cent cent cent Heat 101416 Ten- Elougfi 12.4. BHN Thermal historyfiF;

N sile' hom's'cooling" 28.1. 54j7' 96.1 23.0 20.0 "196 As'cast: 24856 105.5 4855 37.3 174 2000+2-WQ. 82.2 132.0 13.5 17. 293 2000 2WQ-ll400 6-VVQ. 106.2 143.0 7.5 12.2 332 20002WQ+18006W'Q,. 110.1 143.0 10.0 11.8 332 20002WQ+13002W Q.; 107.5 132.5 17.5 23.3 262 .2000-2-WQ,+l200 8WQ. 108.3 1 133.0 21.5 27.8 286 i2000-2-WQ+12004W.Q;-.-. 29--- 56.0 98.2 "27.5 31.6 "'QOTAscast."

49.6 102.0 44:0 34.4 .22 8' 20002-'WQ,;, 81.9 133.0 13.5, 17.0 .286. 2.000 .2.WQ+1400;6-WQ. 110.4 147.0 8.5 12.2 332 2000-2-WQ+13006WQ. 112.1 145.0 0.5 13.4 302 2000-2-W.Q+1300-2-W.Q.J 99.0 1127.5 21.0 29.3 203 2000-2-W +1200.-8-W,Q. 104.8 151.0 23.5 26.8 277 2000-2-WQ+1200-4-WQ. 37.'.'- 55.4 103:2 31.5 31.5 196'" As'casti' 48.2 106.1 46.0 375' 183. 2000-2-W 86.5 138.0 14.0 15.2 170 2000-2-WQ.+1400-6-W 101.0 144.0 11.0 14.5 302 2000 2WQ.-i-.1300-6WQ.. 91.4 119.6 18.5 23.2 270 2000-2-W +1200-8-W See footnotes, Table I. 7

TABLE III Precipitation 1 H ardenable M angimes 'Stecls- With 0.5 Carbon Chemical composition Hent-No.- o,- Mn, 81, Cr, N1, M0, v, v 1 .41. I

per perper 'perper 'DEF- percent cent cent cent cent cent cent 0.54 2.06. 2:04 0.55 0.04 .062]: l 0.49 2.08 2.07 0.83 Max: .051

Heat YS 'IS Elongi RA. BHN Thermal history, F.,

No. hours cooling 50.6 115.8 59.0 44.0 174 2000-24VQ. 87.0 141.5 14.0 17.0 286 2000- W +1400-6-W 111.6 154.0 10.0 15.2 332 2000-.-W +1300-6 W 104.1 148.5 13.5 16.0 321 20002WQ+1300-2WQ. 84.0 140.0 20.5 20.2 286 20002-WQ+1200-8WQ 10 24-.- 60.0 99.5 19.0 23.4 I 228 As cast.

52.8 114.0 43.5 35.0 207 2000-2-WQ. 96.6 144.0 7.0 3.5 321 2000-2-W +1400-6-W 128.7 169.0 5.5 0.6 351 2000-2WQ+13006WQ. 120.6 142.5 9.5 14.8 230 2000-2-W +1200-8-W 99.3 130.5 21.5 27.5 .277 2000-2-WQ,+1200 2WQ. 05.6 127.0 29.5 28.8 262 2000-2WQ+10S0-8-WQ,. 261' 66.5 106.3 19.5 19.9 223 Ascast.

55.3 105.7 35.5 30.9 200 20002WQ. 96.0 130.5 6.0 9.6 311- 20002WQ+14006-WQ. 126.0 153.0 5.0 3.5 1 351 20002WQ+l300-6-WQ. 120.9 137.5 :10. 5 13.4 302 2000-2-WQ+12008-WQ. 102.0 129.5 20.5 22.7 293 2000-2-W +1200-2-W 194.2 128.0 29.0 32.1 277 20002WQ+10S08WQ.

See moraines; TablIi n win be seen from the foregoing that 'under th'e' pres; ent" invention, we" are able "to increase significantly; by

precipitation "hardening, the yield strength in a standard the best balance of yield and elongation, and holding vanadium tobetween about-034.9%. It is'moreo'ver important-to *observe'that precipitation hardening can be accomplished efliciently and at low cost because inseveral instances the'hardening is produced after only two to'four hours of heat treatment;

The-alloy-is further characterized by nickel contents of about 2 to 6%. Thurs, nickel can be as low as about 2% provided about 2% of molybdenum is present; but" 3% nickel (heat 342; 51851 005 heat37). produces satis factory'results with molybdenum absent. From this and other datawehave' concluded that the'pr'esent alloyshou'ld containatlea'stf3%"total of nickel and molybdenum."

7 Hence, while we"have illustrated and described pre'-" ferred' embodiments-ofthepresent invention; it is to be understood that these are capable of variation and m0di-' I fication; and=we thereforedo not-wish to be limited to the precise detailsset"fortlnbut desire to avail ourselves of such? changes 555 514555035555.1511 within the purview of: thefollowing claims.

We-clair'n:

1. A11 austeniticmanganese steel alloy containing'about- 13 to 14%-manganesecapable-of-being precipitation hardenedto produce a yield strength of 70,000-p.s.i. (0.2% set)and an elongation of-at least 10% (in 2") and containing carbon restrictedto the range of about 0.4 to 0.7%, vanadium additions restricted to the range of about 0.3 to 0.9%; groupconsis'ting'of (a)' about 3 to 6%nickel and (b) at"least'2%ea'ch'of nickel and'molybdenum' upto a total' nickel-molybdenum content of about 6%, balance essen-' tially iron;

2.'An'-=alloy'according-toclaim' 1 wherein carbon is restricted to thenarrow range of 0.40.'5%carbon, havinga yield strength of--100,000 p.s.i. (0.2% set) and" (in 2"), after pre-' an 'elongation of at least about 20%' cipitation hardening;

page '406, published by John Wiley & Sons, Inc.. New York, N.Y.

and an" addition selected from the 

1. AN AUSTENITIC MANGANESE STEEL ALLOY CONTAINING ABOUT 13 TO 14% MANGANESE CAPABLE OF BEING PRECIPITATION HARDENED TO PRODUCE A YIELD STRENGTH OF 70,000 P.S.I. (0.2% SET) AND AN ELONGATION OF AT LEAST 10% (IN 2") AND CONTAINING CARBON RESTRICTED TO THE RANGE OF ABOUT 0.4 TO 0.7%, VANADIUM ADDITIONS RESTRICTED TO THE RANGE OF ABOUT 0.3 TO 0.9%, AND AN ADDITION SELECTED FROM THE GROUP CONSISTING OF (A) ABOUT 3 TO 6% NICKEL AND (B) AT LEAST 2% EACH OF NICKEL AND MOLYBDENUM UP TO A TOTAL NICKEL-MOLYBDENUM CONTENT OF ABOUT 6%, BALANCE ESSENTIALLY IRON. 